The instant invention relates to control systems for managing and controlling multiple energy sources.
Commercial, industrial and institutional consumers of energy commonly utilize multiple energy sources to minimize energy costs and ensure security and availability of their energy supply. For example, a predominantly natural gas consumer may store volumes of an alternate fuel, such as a diesel fuel or fuel oil, which may be used to fire process or heating equipment in the event that the gas supply is interrupted, or if the procurement costs of natural gas rises above that of the alternate fuel. Equipment at the facility is usually equipped with appropriate means for introducing either type of fuel to the equipment. Such equipment is usually referred to as a dual-fuel device.
With regard to fuel cost, the cost of a distributed energy source, such as electricity or natural gas, is often related to the stability of a customer's utilization of that fuel. For instance, a consumer of electricity often pays a "demand" charge which reflects the difference between his peak usage and base consumption of electricity. The demand charge is generally interpreted as a capacity charge paid by the consumer for excess capacity to be reserved for the few times it is utilized.
A similar premium rate structure typically exists for a natural gas customer who generates seasonal or process related peak rates of consumption which are significantly higher than their base consumption rates. The difference between a natural gas customer's peak and base consumption rates is typically referred to as a "load factor." A customer that consumes 1000 Mcf natural gas daily for the months of December, January, and February and then only 700 Mcf natural gas daily for the remaining nine months of the year would be determined to have a load factor of 70%. Based on a load factor of 70%, the customer's natural gas procurement cost might be $5.00/Mcf. If the customer's load was stable all year round at 700 Mcf daily consumption, the load factor would be 100% and the customer's natural gas procurement cost could drop to $3.80/Mcf. The reasons for the difference in cost is that the supplier of the natural gas can predict his customer's consumption more accurately which, in turn, allows him to purchase, and subsequently supply relatively precise volumes of gas at "firm rates", and therefore, demand charges are minimized. Natural gas consumers are thus becoming increasingly more aware of the benefits that can be realized by managing their load factors more efficiently.
The instant invention provides an automated control system for monitoring a primary fuel source of a dual-fuel apparatus, and for automatically switching from the primary fuel source to a secondary fuel source when a predetermined amount of the primary fuel is used in a measured time period, the object of the invention being to automatically maintain a 100% load factor of the primary fuel based on the measured time period. The control system generally includes a meter mounted in the primary fuel line for continuously monitoring consumption of the primary fuel and for outputting an electronic flow signal representing consumption of primary fuel. The flow signal is received by a programmable logic controller having a real-time clock whereby consumption of the primary fuel is measured against time. The control system further includes remote control actuated valves mounted in the primary and secondary fuel lines for selectively controlling the flow of the primary and secondary fuels to the dual-fuel apparatus. The programmable logic controller is programmed with a set of control parameters, including a measured time period, and a 100% load limit of fuel consumed during the given time period. The programmable logic controller sums the flow signal over the 24 hour period and automatically controls actuation of the first and second valves to switch from the primary fuel to the secondary fuel when the 100% load limit is achieved. When the 24 hour time period expires, the logic controller actuates the valves to revert back to the primary fuel and starts the measured time period over. The present system thereby provides the ability to automatically maintain a consistent daily use of the primary fuel source.
In the preferred embodiment as described in detail herein, the control system is utilized in connection with a dual-fuel steam boiler, wherein the primary fuel is natural gas, and the secondary fuel is fuel oil. The meter is operative for measuring natural gas flow and generates a scalable pulse-train signal which is generated proportionately with gas consumption. The programmable logic controller is utilized to receive and sum over a 24 hour period the volume proportional pulse-train signal emitted by the gas meter. When the time based volume of gas has reached a predetermined load limit, the flow of gas to the boiler is stemmed by closing the valve in the primary gas line, while a flow of oil is initiated by opening the valve in the secondary oil line. The boiler then operates on the fuel oil until a new period of measurement is initiated, or until the system is manually overridden. The system then reverts back to natural gas fuel when the new measured time period commences.
Accordingly, among the objects of the instant invention are: the provision of an automated control system for managing multiple energy sources to maintain a 100% percent load factor of a primary fuel source; the provision of an automated control system for monitoring a primary fuel source and for automatically switching from the primary fuel source to a secondary fuel source when a predetermined amount of the primary fuel is used in a measured time period; and the provision of such a control system which is particularly useful in connection with the management of natural gas consumption rates.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.